The field of the present invention is expansion joints for ducting and flue systems, and more particularly, nonmetallic flexible expansion joints to provide stress relief in refactory lined flue systems used in high temperature applications such as power generation and related activities.
In power generating or cogeneration plants, including facilities for obtaining usable electrical power or processing steam/hot water from the burning of solid, liquid or gaseous fuel products, hot flue gases generated by the combustion process are typically directed through a series of processing areas to remove particulates and environmentally hazardous components before finally being exhausted from the facility. FIG. 1 illustrates a power generation plant of unique design that includes a furnace having a circulating fluidized bed (CFB) wherein various fuel materials are combusted. The hot flue gases containing combustion by-products are transferred from the furnace through a flue/expansion joint to a cyclone separator. The cyclone separator diverts heavier combustion particulate matter back to the CFB and the fine particulate matter and hot flue gases are directed through a heat exchanger. The fine particulate matter is then diverted to a particulate filter for disposal. Gases emitted from the facility will have most of the combustion by-product emissions, including NO.sub.x, SO.sub.2, CO, particulates, etc., removed therefrom, resulting in an environmentally safe means of power generation.
Nonmetallic flue expansion joints are flexible connectors designed to provide stress relief in flue systems by absorbing movement caused by thermal changes. They also act as vibration isolators, and in some instances, make up for minor misalignment of adjoining flues or equipment. They may be fabricated from a wide variety of nonmetallic materials, including synthetic elastomers, fabrics, insulation materials and other suitable materials depending upon the designs thereof. Since their introduction in the early 1960's, the use of nonmetallic expansion joints has continuously grown. The advent of more rigid emission standards has caused the use of more complex flue work systems. Nonmetallic expansion joints have been used in place of the traditional all metal expansion joints to solve problems caused by the thermal and mechanical stresses generated in these complex systems. Although the major user of the nonmetallic joint continues to be the power generation industry, the use of this product has expanded into many other industries wherein gases are conveyed including pulp and paper plants, refineries, steel mills, foundries, smelters, cement plants, kilns, refuse incineration, marine applications, vapor-heat-dust recovery, food processing, and HVAC (Heating, Ventilating and Air Conditioning).
A typical prior art nonmetallic expansion joint is shown in FIG. 2. The joint includes a pair of angle brackets mounted to the respective ends of a pair of adjoining ducts or flues. A pair of frame members are in turn attached to the angle brackets. The frame members have mounted thereto a flexible pressure seal that extends around the periphery of the expansion joint. The pressure seal may be of the elastomeric type for operation below 400 degrees F or may be of the composite type for operation at temperatures continuously above 400 degrees F. It will be appreciated that the flexible pressure seal allows relative axial, transverse, angular and rotational movement between the respective ducts while preventing the escape of pressurized flue gasses and particulates carried therein. Other nonmetallic expansion joint constructions may be seen in the "Technical Handbook" published by the Ducting Systems Nonmetallic Expansion Joint Division of the Fluid Sealing Association, 2017 Walnut Street, Philadelphia, Pa. 19103 (2nd Edition), the contents of which are fully incorporated herein by this reference.
It is known that nonmetallic expansion joints are prone to failure from the build-up of abrasive particulates carried by the flue gas stream, which can accumulate in the expansion joint in such quantities that they eventually rupture the pressure seal. Moreover, fly ash and other particulates can cause damage to the expansion joint by solidifying to a cementatious state. Also, certain non-cementatious particulates (fly ash) can create a severe, corrosive (acidic) environment when subjected to cooling (below the H.sub.2 SO.sub.4 dew point) during a maintenance outage.
To prevent premature expansion joint failure from the build up of particulate matter therein, baffles have been proposed to help direct particulate matter beyond the expansion joint, as shown in FIG. 2. Other proposals include mounting the flexible pressure seal substantially flush with the interior surface of the duct or flue, as shown in FIG. 3, or mounting an insulation barrier behind a baffle arrangement as shown in FIG. 4. Although these proposals may exhibit varying degrees of effectiveness in minimizing expansion joint failure, the arrangement of FIG. 3 may result in thermal transfer on the inner face of the expansion joint and abrasion from particulates in the gas stream. A greater setback would be desirable. The arrangement of FIG. 4 may result in the insulation barrier rubbing on the baffle under negative pressures. Moreover, the insulation barrier must be fixedly attached to both sides of the joint, which may complicate joint construction and also impart adverse loads on the barrier.
Accordingly, there is an evident need for an expansion joint flexible seal which not only prevents particulate build up, but which is durable, easy to install and will perform satisfactorily despite joint movement. It would be further desirable to provide an expansion joint flexible seal that also performs a sealing function to provide an additional gas sealing barrier.
The present invention accomplishes the foregoing objects and advantages. It is therefore an object of the present invention to provide an improved expansion joint and flexible seal therefor.
It is a further object of the present invention to provide an expansion joint having a flexible seal that is not adversely affected by relative joint movement.
It is a further object of the present invention to provide an expansion joint having a modular construction for easier installation.
It is a further object of the present invention to provide an expansion joint and flexible seal therefor providing an additional gas sealing barrier.